1. Field of the Invention
The present invention relates to control of vehicle mounted, engine driven generators for the purpose of stabilizing frequency and voltage characteristics of generator output. The invention finds applications in vehicles equipped with electrically operated auxiliary apparatus dependent upon stable alternating current (AC) electrical power, wherein ground vehicles, boats, and aircraft are provided with generators driven by the prime power-plant of the vehicle. Examples of vehicles which could benefit from incorporating the invention include rescue and military vehicles having AC powered communications equipment, utility and telephone company repair and maintenance vehicles, vehicles providing electrical welding equipment, and other vehicles utilizing AC equipment powered directly from an engine driven AC generator.
2. Description of the Prior Art
Many vehicles carry aboard equipment which is electrically operated by alternating current. Ordinary vehicular generators-are typically designed to convert AC output to DC for the purpose of charging the battery, and for supplying originally installed vehicular electrical equipment which is DC operated for compatibility with a battery based vehicle electrical system. As functions of vehicles have been increased over the years, it has become possible to drive an auxiliary generator from the engine or principal power plant of the vehicle. Typically this is accomplished by connecting the generator to a power take off or to any other suitable point of connection to engine output. While this will indeed operate a generator, variations in engine speed will wreak havoc with characteristics of power output and therefore with equipment which is dependent upon stable voltage and frequency characteristics of electrical power.
U.S. Pat. No. 4,287,429, issued to Oleg I. Bashnin et al. on Sep. 1, 1981, sets forth a control circuit for controlling the output of a hydraulically driven generator. The hydraulic circuit of Bashnin is appropriate for a large scale hydroelectric generator, but lacks structure appropriate for a motor vehicle mounted generator, as seen in the present invention. Notably, a small hydraulic motor, oil filter, oil tank, oil cooler, and small hydraulic controls are not shown in Bashnin.
U.S. Pat. No. 5,028,221, issued to Jean Malfit on Jul. 2, 1991, sets forth an improved generator receiver which is a mechanical component disposed in the power train of a generator. This mechanical component lacks a control scheme including a comparison circuit and a master spool valve for assuring that the driven element rotate at constant speed, as seen in the present invention.
U.S. Pat. No. 5,421,705, issued to Hartmut, Benckert on Jun. 6, 1995, describes a safety limit control for a concrete pump. The control limits the amount of concrete being pumped to avoid stalling of a diesel power plant. The system of Benckert does not vary hydraulic output of a pump such that the output to an associated hydraulic motor is constant despite fluctuating input speeds from the motor. The control scheme of Benckert lacks the comparison circuit and hydraulic circuit of the present invention.
U.S. Pat. No. 3,941,016, issued to Gerhard Will on Mar. 2, 1976, describes a hydraulic pressure generator which produces pressure responsive to engine speed. Logic of operation is opposite that of the present invention. Will provides a variable output for the purpose of assisting in determining when to cause an automatic transmission to change gears. The present invention provides a constant output regardless of input speed from the engine so that the element driven by the engine rotates at a constant speed.
U.S. Pat. No. 5,410,943, issued to Gilbert Kervagoret on May 2, 1995, sets forth a progressively opening control valve for a motor vehicle anti-skid braking system. This valve lacks the control system as seen in the present invention, which control system includes a comparison circuit utilizing a rotational speed sensor and a reference source. The valve of Kervagoret is a single component of a hydraulic circuit, rather than comprising a complete circuit as seen in the present invention.
The need for controlling speed of an AC generator mounted in a motor vehicle, wherein the principal engine of the vehicle also drives the generator, has not been answered in the prior art. None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.
The present invention provides a control scheme for assuring that a generator carried aboard a motor vehicle and driven by the principal power plant of the motor vehicle be driven at constant speeds. This is an important condition for assuring proper operation of AC operated equipment carried aboard the vehicle. In vehicles wherein an AC generator is powered by the engine of the vehicle, variations in engine speed threaten to disrupt operation of equipment dependent upon stable voltage and frequency characteristics of the electrical power. Since engine speeds vary with demand for power to propel the vehicle, the novel control scheme provides a hydraulic system which operates the generator at constant speeds despite variations in engine speeds.
This is accomplished by providing a hydraulic pump coupled to the output of the engine of the vehicle, and driving a hydraulic motor therefrom. The generator is driven by the hydraulic motor. A control valve assembly is interposed between the hydraulic pump and the hydraulic motor to apportion pressurized hydraulic fluid from the pump such that the hydraulic motor receives a constant flow rate. A control circuit senses operating conditions and controls the control valve assembly appropriately to maintain the constant flow rate.
Auxiliary functions of the system include providing gradual acceleration of the generator when starting from the stopped condition, adjustment of generator output characteristics, and cooling of hydraulic fluid. Gradual acceleration or xe2x80x9csoft startxe2x80x9d mitigates or eliminates damage which might otherwise result from abrupt connection to engine power. The period of acceleration from the stopped condition to full speed is adjustable within a range of ten seconds to one minute, and may be controlled by a human operator of the system. Combined with protection from fluid overheating, the motor, seals, fluid conduits, and control valves are protected from damage associated with viscous fluid.
A particularly advantageous feature of the invention is that the control valve assembly meters fluid flow in both inlet and outlet directions, thereby maintaining pressure drop on both sides of the control valve assembly almost equal. This increases efficiency by reducing heat and power losses, and assists in virtually eliminating overspeed and underspeed of the generator as conditions change.
The apparatus is self-contained and readily retrofit to a motor vehicle having a power take-off. The apparatus includes a circuit breaker so that, combined with ability to manage generator speed and to limit fluid temperatures, the apparatus is self-protecting. A display annunciates output voltage, output frequency, output amperage, generator rotational speed, and elapsed time of operation.
Accordingly, it is one object of the invention to provide control of a generator driven by the engine of a motor vehicle such that generator speed and hence electrical output remain constant despite fluctuations in engine speed.
It is another object of the invention that the control system virtually eliminate overspeed and underspeed as the system adjusts fluid input to the hydraulic motor driving the generator responsive to fluctuations in speed of the engine of he motor vehicle.
It is a further object of the invention that the apparatus be self-protecting from damage to overpressure and overtemperature of pressurized hydraulic fluid.
Still another object of the invention is to provide annunciation of generator output characteristics.
An additional object of the invention is that the apparatus be self-contained and readily retrofit to motor vehicles having power take-offs.
It is still a further object of the invention that acceleration of the generator from the stopped condition be gradual.
Yet another object of the invention is to provide selectively variable time of acceleration of the generator from the stopped condition to full operating speeds, and to enable a human operator to select the rate of acceleration.
It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.